This invention relates to a method and device for controlling sound emission in an automatic performing piano, and more specifically to such a piano which is immune from inaccuracy of performance in sound reproduction due to the time lag of emission of sound caused by variations in intensity of depressed keys.
A conventional automatic performing piano has suffered from imbalance of sound emission timing between strong strokes and weak strokes. This is due to the time period from a depress-key command (on-event) to actual emission of sound during which a solenoid is energized.
Some prior art methods try to solve this problem by adopting a sound prohibited time period T1, FIG. 12, in designing the amount of electric power L.sub.drv to be supplied to the solenoid for depressed keys. In FIG. 12, L.sub.1 is an original voltage level, L.sub.2 a start-up voltage level, and L.sub.3 is a holding voltage level. T.sub.2 is a time period to sustain the start-up voltage level. The sound prohibited time period T.sub.1, as shown in FIG. 12, is provided at the first stage of the chart of electric power L.sub.drv in order to correct the emission timing. The sound prohibited time period T.sub.1 is determined according to depression intensity data included in depression data such that the stronger the stroke is, the longer the duration of sound prohibited time period T.sub.1. The maximum value of the sound prohibited time period T.sub.1 is 100 milliseconds.
However, determination of the sound prohibited time period T1 simply according to the depression intensity data results in the following two undesirable phenomena.
One is a "reverse phenomenon" which is often caused by one strong but short key stroke. Since the sound prohibited time period T1 drags on because of the intensity of the key stroke, the off-event command in response to the release of the same key may precede the start up of the driving power. In reproduction of hora staccato notes, with a sound emission time period of only 30 milliseconds for each of the key strokes, this "reverse phenomenon" may occur, thus resulting in failure to reproduce the performance.
The other undesirable phenomenon is an "overlap phenomenon". When a strong key stroke on one key is immediately followed by a weak key stroke on the same key, the off-event for the strong key stroke may be caused after the expiration of the sound prohibited time period T1 for the weak key stroke, thus hampering reproduction of successive key strokes on the same key.